This invention relates generally to nuclear reactors and more particularly, to a seismic load suppressing system that includes seismic isolators and displacement limiters.
In at least some known nuclear reactor power plants, the reactor vessel is supported by a substantially stiff pedestal. The pedestal is in turn supported by the reactor building basemat which rests below ground and may rest on bedrock. As a consequence of this arrangement, the fundamental frequency of the assembly including the reactor and the reactor pedestal is approximately 4 hertz (Hz). The fundamental frequency of 4 Hz is in an intense frequency region of earthquake excitation, making the assembly susceptible to seismic motion. The plant design parameter Safe Shut-down Earthquake (SSE) typically has a value of 0.3 g, i.e., 0.3 times the gravitational acceleration, for a standard nuclear power plant (g=9.81 meters/second squared). At an SSE equal to 0.3 g, the safety related equipment can be shut down and survive when forces of 0.3 g are encountered by the plant. At sites where forces in excess of 0.3 g are anticipated, the standard plant design needs to be modified to accommodate the higher seismic forces. One problem that must be addressed in the design of the plant is that the response to a seismic input of the reactor internal components, including the fuel, will generally be magnified. For example a seismic input of 0.3 g may result in a response by the fuel in the reactor of 0.9 g.
It would be desirable to provide a nuclear reactor that can filter out high seismic excitations to allow for a standard plant design to be site independent and to lower the response of reactor internal components, including the fuel.